linux-kernel - [RFC PATCH 4/7] KVM: x86: SVM: Pass through shadow stack MSRs

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Date:   Wed, 12 Oct 2022 20:39:07 +0000
From:   John Allen <john.allen@....com>
To:     <kvm@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <pbonzini@...hat.com>,
        <weijiang.yang@...el.com>, <rick.p.edgecombe@...el.com>,
        <seanjc@...gle.com>, <x86@...nel.org>, <thomas.lendacky@....com>,
        John Allen <john.allen@....com>
Subject: [RFC PATCH 4/7] KVM: x86: SVM: Pass through shadow stack MSRs

If kvm supports shadow stack, pass through shadow stack MSRs to improve
guest performance.

Signed-off-by: John Allen <john.allen@....com>
---
 arch/x86/kvm/svm/svm.c | 17 +++++++++++++++++
 arch/x86/kvm/svm/svm.h |  2 +-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 411c815d2d91..f40d3df2c1be 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -134,6 +134,13 @@ static const struct svm_direct_access_msrs {
 	{ .index = X2APIC_MSR(APIC_TMICT),		.always = false },
 	{ .index = X2APIC_MSR(APIC_TMCCT),		.always = false },
 	{ .index = X2APIC_MSR(APIC_TDCR),		.always = false },
+	{ .index = MSR_IA32_U_CET,                      .always = false },
+	{ .index = MSR_IA32_S_CET,                      .always = false },
+	{ .index = MSR_IA32_INT_SSP_TAB,                .always = false },
+	{ .index = MSR_IA32_PL0_SSP,                    .always = false },
+	{ .index = MSR_IA32_PL1_SSP,                    .always = false },
+	{ .index = MSR_IA32_PL2_SSP,                    .always = false },
+	{ .index = MSR_IA32_PL3_SSP,                    .always = false },
 	{ .index = MSR_INVALID,				.always = false },
 };
 
@@ -1174,6 +1181,16 @@ static inline void init_vmcb_after_set_cpuid(struct kvm_vcpu *vcpu)
 		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_EIP, 1, 1);
 		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_ESP, 1, 1);
 	}
+
+	if (kvm_cet_user_supported() && guest_cpuid_has(vcpu, X86_FEATURE_SHSTK)) {
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_U_CET, 1, 1);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_S_CET, 1, 1);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_INT_SSP_TAB, 1, 1);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PL0_SSP, 1, 1);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PL1_SSP, 1, 1);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PL2_SSP, 1, 1);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PL3_SSP, 1, 1);
+	}
 }
 
 static void init_vmcb(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 6a7686bf6900..c1c3e090ff9d 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -29,7 +29,7 @@
 #define	IOPM_SIZE PAGE_SIZE * 3
 #define	MSRPM_SIZE PAGE_SIZE * 2
 
-#define MAX_DIRECT_ACCESS_MSRS	46
+#define MAX_DIRECT_ACCESS_MSRS	53
 #define MSRPM_OFFSETS	32
 extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
 extern bool npt_enabled;
-- 
2.34.3